Shielding and balancing means



April 12, 1927.

- 1 624 459 w. J. ADAMS ET AL SHIELDING AND BALANCING MEANS Filed Dec. 13. 1920 2 Sheets-Sheet 1 v /nven7or s: W/W/am J Adams Arf/vur Haddock 4 I eat/ Apnl 12, 1927. w. J. ADAMS ET AL 1,624,459

samwme AND BALANCING umms Filed Dec. 13. 1920 2 Sheets-Sheet 2 mveflfonsi W////am (J Adams Arfhur haddaak Patented Apr. 12, 1927.

. UNITED STATES PATENT OFF-ICE.

WILLIAM J. ADAMS, OF IRVINGTON, NEW YORK, AND ARTHUR HADDOCK, OF EAST ORANGE, NEW JERSEY, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCOR- PORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SHIELDING AND BALANCING MEANS.

Application filed December13, 1920. Serial No. 430,429.

This invention relates to duplex transmission systems and methods of duplex transmission utilizing a single conductor for transmission and reception, and more particularly to improved features of such systems whereby the transmitted energy is more perfectly excluded from the receiver. A radio system as described herein serves to illustrate the principles involved. These principles may be applied in constructing apparatus for use in various types of systems.

In certain types of radio systems for duplex transmission wherein a transmitter and a receiver are connected to an antenna conjugately with respect to each other, it is desirable that the amount of energy which passes into the receiving circuit from the transmission circuit, be maintained at a minimum. The present invention comprises improved means for accomplishing this result. In such systems, the electromagnetic effect of the transmitted waves on the receiver is balanced as perfectly as possible. Owing to the facility with which high frequency energy is transferred from the transmitting circuit to the receiving circuit by inherent electrostatic coupling, it becomes necessary to reduce the transfer of energy in this manner. To this end the transmission and reception circuits are shielded from each other as perfectly as possible. A shielded lead block is provided for this purpose. Means is also provided for maintaining electrostatic balance as well as electromagnetic balance. 1

A further feature consist-s in the provision of means whereby the primary and secondary of the transformer which transfers 7 energy to the receiving systems are shielded from each other. An annular or toroidal shield provided for this purpose contains the primary coil while the secondary is mounted in the central portion of the shield.

The invention will be more particularly described in connection with the accompanying drawingswherein Fig. 1 is a view show ing in perspective the mechanical arrangement of the shield and balancing means; Fig. 2 is a circuit diagram of the circuit ele ments of Fig. 1; while Fig. 3 is an exploded or extended view of the shielded lead block and its supporting bracket.

The receiving circuit may be traced by referring to either Figs. 1 and 2:--From a receiving antenna 1, thehigh frequency waves are conducted into a receiving circuit comprising condenser 2, conductor 3, conductor 4, the contiguous half of coil 5 to the midpoint tap, connected to conductor 9, thence through the other half of coil 5, the conductor 6, conductor 7, condenser 8 and the balancing network AL constituting an artificial antenna or artificial line to ground. The current traversing the coil 5 passes through all the turns in the same direction. lrlowever, a portion of the. received current leaves the coil 5 at the mid-tap and passes through the transmitting circuit 9. thereby traversing only a portion of the turns 01' the coil 5. The two halves of the coil 5 are in series aiding relation with respect to received current and consequently their electromagnetic effects on coil 10, due to received currents are cumulative. A tuning condenser 11 shuntedaround the coil 10 serves to adjust the circuit 10, 11 to reasonance at the frequency of the waves being received. The energy in the circuit 10, 11 acts upon the receiving system B- .which may conveniently comprise a thermionic detector 1) whose output circuit is coupled by the transformer 12 to a receiving or translating device 13, illustrated in the present instance as a telephone receiver. A tuning condenser 14 for varying the natural wave length of the antenna in receiving, is shunted around thecoil 5. By varying this condenser the natural period 'of the antenna is made to coincide with the period, of the received waves. 7

is connected to an intermediate part of the coil 5. High frequency currents flowing through the conductor 9 will pass through the turns of the coil 5, art in one direction and part in another. art of this current willflow through the radiating antenna 1,

ion

while the other part will flow through the artificial antenna AL. The manner of constructing suitable artificial antennae t balance various types of radiating antennas is known to those skilled in the radio art. In the simplest case, if the coil 5 is divided into two similar equal groups of turns, and the artificial antenna consists of impedance elements producing an effective reactance and resistance identical with the reactance and resistance of the antenna, the effect of the outgoing current upon the coil will be negligible since the field produced by current in one-half of the turns of coil 5 will be neutralized by that produced by current in the other half of the turns. In this case one-half of the transmitted energy will be consumed in the artificial line. For a short range system utilizing comparatively low power. this is not a very serious objection. Less than half of the transmitter energy may be consumed in the artificial antenna by increasing its impedance and resistance relative to that of the radiating antenna and correspondingly adjusting the number of turns in the two parts of the coil 5 so that balance will be secured. hen a condition of balance is attained, the transmitted waves will produce no difference of potential across the terminals of the condenser 14. By varying this condenser, it will therefore be possible to tune the antenna for received waves independently of the particular wave length being used for transmission. T ransmission. and reception may be carried on simultaneously or successively at different wave lengths. Either the transmitting wave length or the receiving wave length may be changed within certain limits independently oi the other provided the construction of the artificial line is such that reasonably accurate balance is attained for each wave length used for transmitting.

It has been found that the capacity and mutual inductance between the conductors :1, at and the conductor 9 and between conductors 6, 7 and conductor 9 have a substantial effect in transferring energy and if these capacities are not accurately balanced, an undesired transfer of energy into the receiving circuit will result. In order to secure this balance, the conductors 3, T are twisted together and passed through a conduit 18, (Fig. 3) in a shielded lead block 19. while the conductors 4 and 6 are twisted together and passed through a. conduit in the same block. The conductor 9 is passed through conduits 21 and 22 in the lead block, thereby being maintained at the same distance from each member of each of the pairs of twisted conductors. Orifices 23 and 24 are provided, through which are extended the terminals of the conductors 3, 4, 6 and 7 for attachment to the binding posts 25 and 26 of the condenser 14. These binding posts are placed as near to the orifices 23 and 24: as the mechanical construction of the parts will allow. For convenience, orifices 27 and 28 are provided through which extends a small portion of the conductor 9. This feature, however, is one of convenience in mechanical construction rather than necessity since the conductor 9 might be embedded in the lead block throughout its length. The lead block consists of a body of insulation material comprising any convenient number of parts 29, held together in any convenient manner as, for example, by the brass screws 30. A conductive shield 31 of nonanagnetic material surrounds the entire lead block. Bracket 32 supports the lead block adjacent the binding posts 33 on the coil 5, and likewise supports the condensers and 8 imn'iediately adjacent and symmetrically disposed with relation to the orifices 34 and The antenna 1, transmitter T and artificial antenna AL are connected to the system through binding posts 36. The exposed portion of the conductor 9 and the portions of the conductors between the binding posts 36 and the condensers 2 and S are protected by grounded non-magnetic shields. The transmitter T and the artificial antenna are also surrounded by grounded shields as illust-rated. This shielding is for the purpose of preventing any electrostatic transfer of energy from any part of the transmitting circuitto the receiving circuit. Condenser 14 is also surrounded by a grounded shield.

The coil 5 is wound upon a spool 3T of insulating material, the spool being provided with flanges 38 to space the coil on all sides away from the surrounding annular shield 39. The shield 39 is illustrated as annular but may be oi any convenient shape to adequately house the coil 5. As used in this specification, the term annular is to be construed as including any shield of substantially the same shape and function, such as, for example, a toroidal shield. The shield 39 consists of non-magnetic conductive material and is supported by a bracket 40. Brackets 41 mounted upon the shield 39 serve to support the rotatably mounted coil 10. The coil 10 may be adjusted by rotating its axis relative to the axis of the coil 5 for the purpose of varying the coupling between them. An arm 42 rigidly attached to the spool upon which coil 10 is wound moves over a segment 43 to which it may be secured in any desired position of adjustment by a thumbscrew 44. The shield 39 is grounded through the bracket as illustrated at 45. A radial slot 46 is cut in the shield to break its continuity so that it will not act as a short-circuited secondary for the primary 5. This slot should be comparatively narrow, for example, not more than a few millimeters in width so as to expose as little as possible of the coil 5. It will be seen that the coils 5 and 10 are shielded from each other in an effective manner while at the same time the transfer of energy from the coil. 5 to the coil 10 by electromagnetic induction is not materially interfered with. A grounded shield completely surrounds the receiver and the shield 39, as illustrated in dotted lines.

The novel features believed to be inherent in the invention are set forth in the appended claims.

lVhat is claimed is:

1. Means for preventing sidetone in a duplex high frequency system con'iprising a single open-circuited antenna a transmitter and a receiver operatively connected to said antenna, said receiver including means for balancing the electrostatic effect of the transmitter circuit on the receiver circuit with an equal. and opposite electrostatic effect, and means for simultaneously balancing the clectromagi'ietic effect of the transmitter circuit on the receiver circuit with an equal electromagnetic effect.

2. In a duplex radio system, an electrical element common to the transmission and reception circuits, a lead in said transmission circuit to an intermediate point on said element, a pair of leads from said element to an antenna and an artificial antenna respectively, and conduits of insulating material spacing said last mentioned leads similarly with respect to said first mentioned lead.

3. In a duplex system, a transmission cir cuit lead, an antenna circuit lead and a balancing circuit lead, said two last menti oned leads being equi-distantly spaced from said first mentioned lead, and a grounded shielding means spaced from and shielding all. of said leads.

4. A duplex signaling system comprising a receiving coil, an antenna and an artificial antenna, leads connecting said antennae to the two terminals of said coil, a tuning condenser connected across said coil, a transmitting circuit lead connected to said coil, and means for spacing the leads interconnecting said coil and said antennae equidistantly from said transmitting circuit lead.

5. A combination according to claim il, pavling a conductive shield surrounding said eat 6. A duplex signaling system comprising a receiving coil, an antenna and an artificial antenna, means connecting said antennae with said coil, a tuning reactance connected across said coil. a transmitting circuit lead connected to said coil, and means for spacing the leads interconnecting said coil with said antenna and said artificial antenna, respectively, equidistantly from said trans mitting circuit lead.

'7. In a combination according to claim 6, a conductive shield surrounding said leads.

In witness whereof, we hereunto subscribe our names this 7th day of December A. D., 1920.

WILLIAM J. ADAMS. ARTHUR HADDOCK. 

